Cis Ubuntu2004 V300 7 2 5

7.2.5 Ensure no duplicate UIDs exist (Automated)

Profile

• Level 1 - Server
• Level 1 - Workstation

Description

Although the useradd program will not let you create a duplicate User ID (UID), it is possible for an administrator to manually edit the /etc/passwd file and change the UID field.

Rationale

Users must be assigned unique UIDs for accountability and to ensure appropriate access protections.

Satisfies: SRG-OS-000104-GPOS-00051, SRG-OS-000121-GPOS-00062, SRG-OS-000042-GPOS-00020

Impact

None

Audit Procedure

Command Line

Run the following script and verify no results are returned:

#!/usr/bin/env bash

{
    while read -r l_count l_uid; do
        if [ "$l_count" -gt 1 ]; then
            echo -e "Duplicate UID: \"$l_uid\" Users: \"$(awk -F: '($3 == n) { print $1 }' n=$l_uid /etc/passwd | xargs)\""
        fi
    done < <(cut -f3 -d":" /etc/passwd | sort -n | uniq -c)
}

Expected Result

No output should be returned.

Remediation

Command Line

Based on the results of the audit script, establish unique UIDs and review all files owned by the shared UIDs to determine which UID they are supposed to belong to.

Default Value

N/A

References

1. NIST SP 800-53 Rev. 5: CM-1, CM-2, CM-6, CM-7, IA-5
2. NIST SP 800-53A :: IA-2.1

Additional Information

You can also use the pwck command to check for other inconsistencies in the /etc/passwd file.

CIS Controls

MITRE ATT&CK Mappings: